Pyrite and tramp iron removal apparatus for coal pulverizers



May 5, 1970 G. c. WHITNEY, JR

PYRI'I'E AND TRAMP IRON REMOVAL APPARATUS FOR COAL RULVERIZERS Filed June 29, 1967 F'lG.

I N VEA 'Y L' R GILBERT C. WHITNEY, JR /92% y ATTORNEY United States Patent O 3,510,071 PYRITE AND TRAMP IRON REMOVAL APPARA- TUS FOR COAL PULVERIZERS Gilbert C. Whitney, Jr., Dansville, N.Y., assignor to Foster Wheeler Corporation, Livingston, N.J., a corporation of New Jersey Filed June 29, 1967, Ser. No. 650,131 Int. Cl. B02c 15/12; B07b 7/02 US. Cl. 241-61 3 Claims ABSTRACT OF THE DISCLOSURE Apparatus for pulversizing raw coal feed stock into comminuted particles which can be conveyed to the combustion chamber of a furnace. Iron pyrite particles and tramp iron fall downwardly and are removed without effecting the upward flow of the powdered coal to the furnace.

BACKGROUND OF THE INVENTION In connection with the operation of relatively large coal-fired furnaces, it is customary to supply a stream of finely powdered coal to the combustion chamber. The raw coal feed stock is usually reduced to comminuted particles in a pulverizer apparatus, and after grinding the feed stock, the pulverized particles are conveyed to the furnace in an air stream. In many types of coal feed stock, iron pyrite particles are present which are usually carried into the furnace with the coal powder. This presents a two-fold problem, in that the iron pyrite particles are combusted in the furnace to air pollutants, such as sulphur dioxide and sulphur trioxide with a portion of the iron pyrite particles being continually recirculated through the grinding mechanism. Accordingly, the recirculating pyrite particles are of a hardness which. makes pulverizing more difficult, in that the volume of material passing under the rollers contains less coal than the proportion of combustable material in the raw feed introduced into pulverizer. Also, the relatively harder pyrite particles cause extensive Wear to the rollers. Thus, it can be appreciated that the iron pyrite particles ultimately add to the air pollution problem, and reduce the capacity of the pulverizing unit.

Through the present invention, means have been provided for removing both the iron pyrite particles and tramp iron from the stream of coal powder, without effecting the main flow of coal powder to the furnace. It is important to be able to vary the feed rate of the powdered coal to the furnace in accordance with the desired operating load, and yet still be able to remove the iron pyrite particles and tramp iron.

SUMMARY OF THE INVENTION In accordance with an illustrative embodiment demonstrating features and advantages of the present invention, there is provided apparatus for pulverizing raw coal feed stock into comminuted particles. The pulverizer comprises a housing including a support on which a grinding unit is rotatably mounted. Means are provided for bringing the raw coal feed stock into contact with the grinding unit, such that a main stream of particles is formed which essentially comprises raw feed stock which has not been pulverized, powdered coal, iron pyrite particles, and tramp iron, with the pyrite particles and tramp iron having a greater density than the raw feed stock and powdered coal. The housing is formed with ice a channel adjacent to the grinding unit for receiving the main stream, and a separation chamber is mounted on the housing in fiow communication with the channel such that the iron pyrite particles and tramp iron are forced into the chamber by centrifugal action created by the grinding unit and a portion of the powdered coal is carried into the chamber by the main stream. A bifurcated input air flow stream is conveyed into the housing and the input air stream includes a first path flowing upward- 1y into the channel for conveying the powdered coal out of the housing and a second path flowing into the chamber. Means are provided in the chamber for regulating the rate of flow of the second path into the channel such that the iron pyrite particles and tramp iron fall downwardly into the chamber and the powdered coal from the chamber is conveyed into the channel.

BRIEF DESCRIPTION OF THE DRAWINGS The above brief description as well as further objects, features, and advantages of the present invention will be more fully appreciated by reference to the following detailed description of a presently preferred but nonetheless illustrative embodiment in accordance with the present invention when taken in connection with the accompanying drawings wherein:

FIG. 1 is a front sectional view of pulverizing apparatus embodying features of the present invention; and

FIG. 2 is an enlarged transverse sectional view of the chamber for removing the iron pyrite particles.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a pulverizing apparatus is shown which is generally designated by the reference numeral 10. It should be understood that the present invention is readily applicable to a variety of pulverizing apparatus, and for the purpose of illustration, has been shown in connection with a ring and roller type unit. The pulverizing apparatus 10 includes a steel housing 12 which is mounted at ground level for enclosing a support 14 on which there is rotatably mounted a grinding unit 16. Raw coal feed stock is introduced into housing 12 through conduit system 18 and follows a flow path indicated by the directional arrows, designated C. The raw coal feed stock C after passing through grinding unit 16 is comminuted into powdered coal P, iron pyrite particles I, and tramp iron T. It should be understood that the raw coal feed stock C is not completely converted into the final powdered coal product P, since a portion of the raw coal feed stock C is not completely pulverized and is returned to the rollers by way of the classifier reject system. A separation chamber 20 is mounted on the exterior of housing 12 in airflow communication therewith for receiving the iron pyrite particles I and tramp iron T. It should be noted that a portion of the powdered coal P is carried into chamber 20, but the major portion of the powdered coal P follows an upward flow path out of the housing 10, as indicated by the directional arrows.

It is preferable to fabricate the housing 12 of a heavy gauge steel structure, to completely enclose the pulverizing unit 14. The housing 12 is defined by an upstanding cylindrical wall 22 which extends from the ground level to a circular upper cover 24 which is formed with a central opening to receive an outlet conduit 28 that is in flow communication with a furnace combustion chamber which is not shown in the drawings. An inlet conduit 30- is coaxially positioned within outlet conduit 28 by means of 3 a bracket arrangement 32 which is mounted on upper cover 24. The bracket 32 is provided with an inlet opening 34 and an outlet opening 36.

The support 14 includes a table 40 which is horizontally positioned in the housing 12 and is rotatably driven about its vertical axis by suitable means such as motor drive 42. A grinding ring 44 formed with an annular grinding recess 46 is mounted for rotation on table 40. A plurality of spaced-apart pressure rollers 48, only one of which is shown in the drawings, for the purpose of clarity, are mounted in housing 12, with the lower grinding surface which is designated 52 being positioned in mating contact with groove 46, and the upper grinding surface engaging a pressure ring 54 that is mounted below a thrust ring 56 by means of compression springs 58. A collar 60 is mounted above thrust ring 56 and supports a reject cone 62 which extends to the bracket 32 and communicates therewith through Opening 36. At least three of the pressure rollers 48 should be provided, and the rotation of the grinding ring 44 translates rotation to the pressure rollers 48.

The separation chamber is integrally formed with an upper conduit 70 which is in flow communication with a necked-down throat conduit 72, and a receptacle 74 in flow communication between throat conduit 72 and a tramp iron cylinder 76. An air valve 78 is formed with a plurality of radial vanes 80 and is journaled in cylinder 76 such that the vanes 80 are in air-tight relation with respect to the inner walls of cylinder 76. The receptacle 74 and cylinder 76 communicate by means of an opening 82 and a lower opening 84 is formed in cylinder 76 for allowing the tramp iron to be removed as air valve 78 rotates. By referring to FIGS. 1 and 2, it can be seen that separation chamber 20 is provided with an entrance opening 86 in receptacle 74 and an exit opening 88 in conduit 70, which communicate with openings of equal area which are formed in cylindrical wall 22. It is preferable to mount the separation chamber 20 on the housing 12 by forming an air-tight butt weld around openings 86 and 88 and the corresponding coextensive openings in cylindrical wall 22. In this manner, air exit opening 88 is positioned in a directly opposite and spaced apart position from the grinding contact zone 52. The separation chamber 20 is provided with a damper plate 100 which is mounted in receptacle 84 by a hinging means 102. When the damper plate 100 is in a fully closed position, the opening 86 is completely blocked. Thus, the damper plate 100 can be tilted forward and maintained at various opened positions.

An air input is introduced into housing 12 by means of an air conduit 106 which is in flow communication with housing 12 and a source of air which is not shown in the drawings. The input air forms a main stream designated by the two directional arrows 108, which branches out into a bifurcated air stream that includes a first path and a second path, designated by directional arrows 110 and 112 respectively. The first path 110 flows into a channel 114 which is adjacent to the grinding contact zone 52, and the second path 112 fiowsthrough entrance opening 88 into the receptacle 74 of separation chamber 20. The rate of air flow in separation chamber 20 is controlled by damper 100 such that the relatively heavy iron pyrite particles I and tramp iron T will be gravity released, downwardly into tramp cylinder 86 and the relatively light powdered coal P will be carried upward through the velocity of second air path 112.

Reference will now be made to a typical sequence of operation of the pulverizing apparatus 10. Accordingly, the raw coal feed stock C is dropped through conduit 30 and is brought into contact with grinding wheels 48. The comminuted material which leaves the grinding zone 52 is essentially comprised of the iron pyrite particles I, tramp iron T, powdered coal P, and feed stock which has not been pulverized. The centrifugal force created by the grinding operation forces the iron pyrite particles I and tramp iron T from grinding contact zone 52 through opening 88 into upper conduit 70. The major portion of the powdered coal P remains in channel 114 and no powdered coal P can find its way into receptacle 74. It is important to note that the rate of flow of the first path 110 can be varied in accordance with the fuel requirements at any given furnace operating conditions, without effecting the operation of separation chamber 20. This is achieved by adjusting damper plate to the proper position such that the second path 112 will have a sufiicient velocity in throat 72 to prevent any coal from passing downwardly into receptacle 74, while allowing for the gravity release of the iron pyrite particles I and tramp iron T into cylinder 76. Accordingly, the powdered coal P passes upwardly along the sides of cylindrical wall 22 as indicated by the directional arrows in FIG. 1. The powdered coal flow path passes through inlet opening 34 into outlet conduit 28, and any of the relatively small amount of undesirable heavy material in the powdered coal flow path such as feed stock which has not been ground, iron pyrite particles 1, and tramp iron T, will fall downwardly through outlet opening 36 into reject cone 62. Thus, the recirculated material will either be further ground in grinding unit 16 or separated in chamber 20.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

What is claimed is:

1. Apparatus for pulverizing a raw coal feed stock into comminuted particles comprising a housing, a support in said housing, grinding means rotatably mounted on said support, and means for conveying said raw coal feed stock into contact with said grinding means such that there is formed a downwardly flowing main stream of said comminuted particles which essentially comprises powdered coal, tramp iron and iron pyrite particles, with said tramp iron and pyrite particles having a greater density than said powdered coal, said housing being formed with a channel adjacent to said grinding means for receiving said main stream, and a separation chamber mounted on said housing in flow communication with said channel such that said tramp iron and iron pyrite particles are forced into said separation chamber by centrifugal action created by said grinding means and a portion of said powdered coal is carried into said chamber by said main stream, means for creating a bifurcated input air stream flowing in a substantially counter direction to said downwardly flowing main stream, said input air stream including a first path flowing upwardly at a constant rate of flow into said channel for conveying said powdered coal out of said housing and a second path flowing into said separation chamber, and means in said chamber for regulating the rate of flow of said second path into said channel with out effecting the rate of flow of said first path such that said tramp iron and iron pyrite particles fall downwardly into said chamber and said powdered coal from said separation chamber is conveyed into said channel.

2. Apparatus according to claim 1 in which said means for regulating said rate of flow of the second path comprises a damper plate movably mounted in said separation chamber.

3. Apparatus according to claim 2 in which said separation chamber is formed with an entrance opening for introducing the second path of said air stream and an exit opening for exhausting said second path, a hinge mounted in said separation chamber above said entrance opening, said damper plate mounted on said hinge for positioning such that said second path will have a sufficient velocity to prevent powdered coal from passing downwardly and Wardly.

References Cited UNITED STATES PATENTS Kuntz 24182 Bell 24l82 X Schwartz 241-58 Ebersole 24l5'8 1- .X

6 1/1952 Roberson 24182 2/1966 Sevin 24l53 X US. Cl. X.R. 

